Skip to main content

Full text of "Practical Organic Chemistry"

See other formats



The flask is attached to an upright condenser in which the
water is kept at a temperature of 30  35. Alcohol and aqueous
vapour condense in the condenser ; the aldehyde, on the other
hand, passes by a tube attached to a 100 c.c. pipette into two
narrow (TOO c.c.) cylinders, one-third filled with the dry ether,
and cooled in ice-water. The aldehyde readily dissolves in the
ether and is rapidly absorbed. If the ethereal solution is now
saturated with dry ammonia gas, the whole of the aldehyde
separates out in the form of colour-
less crystals of aldehyde-ammonia,
CH3.CH.OH.NH2. The apparatus
for preparing the dry ammonia is
shown in Fig. 52. The flask contain-
ing strong ammonia solution is heated
by a small flame, when the gas is
readily evolved and passes up the
tower, which is filled with soda-lime
or quicklime. The ethereal solution
is saturated with the gas, and is then
allowed to stand for an hour.

The ether is then decanted from
the crystals, which are drained at
the filter-pump, washed with a little ether, and finally dried in
the air on filter-paper. Yield of aldehyde-ammonia, 25  30
grams. It may be used for the reactions described on p. 67.

Pure aldehyde may be prepared from the aldehyde-ammonia
as follows : The crystals are dissolved in an equal weight
of water and distilled on the water-bath with a mixture
of ij parts of concentrated sulphuric acid and 2 parts of water,
the receiver being well cooled in ice. The temperature of the
water-bath is gradually raised until the water begins to boil,,
and the distillation is then interrupted. The distillate is de-
hydrated over an equal bulk of calcium chloride, from which it
is distilled in the water-bath, heated to 30. The anhydrous
aldehyde is kept in a well- stoppered bottle.

FIG,  52.

3C2H6(OH) + K2Cr207 + 4H9SO4 = 3C,H4O

Cr,(S04)3 + ;H,0
C2H40 + NH, = CH,CH.OH,NH
2CH8CH.OH.NH2 + H2S04 = 2CH3.CO.H +